Each year 30,000-40,000 new head and neck cancer patients permanently lose their salivary gland tissues following radiation therapy. An additional 1-2 million people in US suffer from Sjogren's Syndrome, an autoimmune disease that causes irreversible destruction of salivary parenchymal tissue. These patients usually suffer from severe oral diseases and their quality of life is greatly compromised. A potential treatment is to use stem cells to regenerate new tissue in the damaged tissue or to reconstruct a gland or mimetic tissue to replace the destroyed tissue. To identify the stem cells in salivary gland tissue, the expression of potential stem cell biomarkers will be examined in (1) human salivary tissues, (2) proliferating tissue of rat salivary glands stimulated with isoproterenol, a beta-adrenergic receptor agonist, (3) regeneration of tissue in rat salivary glands recovering from duct obstruction-induced degeneration, and (4) human and rat cell lines (Aim l). These biomarkers include protein molecules critically involved in early salivary gland development and common stem cell markers in other organs. The potential stem cell markers for salivary gland tissue will be determined by the co-localization of stem cell markers, cell proliferation indicators and salivary gland differentiation markers. In the next step (Aim 2), stem cell populations will be isolated from cultured human and rat cells outgrown from salivary gland explants. These potential stem cells as well as cell lines will be transplanted into a duct obstruction-induced atrophic salivary gland. The growth and differentiation of transplanted cells will be visualized by Green Fluorescence Protein. The morphological organization and expression of stem cells and differentiation markers for each cell type will be monitored. Identification of stem cells within salivary glands is first step toward isolation of these cells to regeneration of new tissue and reconstruct an artificial salivary gland. The impact of this application is not only for salivary tissue engineering but also for understanding salivary gland tumor genesis and development. The results of these studies will ultimately lead to revolutionary treatment of salivary gland diseases.